If an active NetClock NTP server has removed itself as an available time source from the Anycast-capable network, the OSPF router will send a request for replacement to the next nearest NTP server, serving under the same NTP over Anycast address.

As soon as the first NetClock server obtains a valid reference again, it will make itself available to the OSPF router, which will then use it as a time source again, based on the principle of shortest path available.